what to do with a gem once I have installed it

I am a complete newbie to Ruby and Gems. I just wanted to try
out an open source Gem tool for testing, and installed Ruby, then
Gem, and managed to install the test tool I wanted to try out -
cvs-datagen.

My question is, because I don't have the time to learn
everything about Ruby just to try out this tool, which has only
.rdoc documentation attached - how do I run the package?

do I have to create a ruby program that requires this gem? and
if so, what is the quickest way to do that?